package demo;

import java.util.LinkedList;
import java.util.Queue;

class MyStack {//用队列实现栈

    private Queue<Integer> qu1;
    private Queue<Integer> qu2;
    public MyStack() {
        qu1 = new LinkedList<>();
        qu2 = new LinkedList<>();
    }

    public void push(int x) {
        if(!qu1.isEmpty()) {//入栈的元素在空的队列中
            qu1.offer(x);
        } else if (!qu2.isEmpty()) {
            qu2.offer(x);
        } else {
            qu1.offer(x);
        }
    }

    public int pop() {
        if(empty()) {//栈为空
            return -1;
        }

        if(!qu1.isEmpty()) {
            int size = qu1.size();
            for (int i = 0; i < size - 1; i++) {
                int tmp = qu1.poll();
                qu2.offer(tmp);
            }
            return qu1.poll();
        } else {
            int size = qu2.size();
            for (int i = 0; i < size - 1; i++) {
                int tmp = qu2.poll();
                qu1.offer(tmp);
            }
            return qu2.poll();
        }
    }

    public int top() {
        if(empty()) {
            return -1;//栈是空的
        }
        int tmp = -1;
        if(!qu1.isEmpty()) {
            int size = qu1.size();
            for (int i = 0; i < size; i++) {
                tmp = qu1.poll();
                qu2.offer(tmp);
            }
            return tmp;
        } else {
            int size = qu2.size();
            for (int i = 0; i < size; i++) {
                tmp = qu2.poll();
                qu1.offer(tmp);
            }
            return tmp;
        }
    }

    public boolean empty() {
        //两个队列都为空的时候,就是栈为空
        return qu1.isEmpty() && qu2.isEmpty();
    }
}
